POSTGRAD. MED. J. (1965), 41, 748 Postgrad Med J: first published as 10.1136/pgmj.41.482.748 on 1 December 1965. Downloaded from SPLENIC MECHANISMS IN THE PATHOGENESIS OF ANAEMIA A. J. BOWDLER, M.D., B.Sc., M.R.C.P. T. A. J. PRANKERD, M.D., F.R.C.P. from the M.R.C. Research Group in Haemolytic Diseases, University College Hospital Medical School, London, W.C.1. ANAEMIA is not infrequently accompanied by the presence of marrow infiltration. Further, enlargement of the spleen, and in some in- red cell output has 'to be assessed in relation stances, as in the haemorrhagic anaemia of to red cell lifespan, which may also alter after portal hypertension, it is clear that both spleno- splenectomy, and the marrow response to a megaly and anaemia arise from a common shortened red cell lifespan is only imperfectly factor. The reasons for the relationship of known. A frequently quoted figure for red splenomegaly and anaemia are less easily dis- cell production in states of chronic haemolysis cerned in other conditions, such as pernicious is six to eight times the normal rate (Crosby anaemia and iron deficiency states. In a third and Akeroyd, 1952). However, Mollison (1956) group there is evidence for the dependance found output as high as 12 times normal in a of the anaemia on the presence of the enlarged patient with paroxysmal nocturnal haemoglo- spleen, and it is in these that the investigation binuria, and we have investigated a man of of the spleen is most significant in view of the 18 years with antiglobulin-positive autoimmuneProtected by copyright. possibility of correcting the anaemia by splen- haemolytic disease who maintained a haemato- ectomy. crit of 20.5% despite a mean red cell lifespan The role of the spleen in producing anaemia of 3.5 days, indicating a red cell output of has been frequently discussed in terms of two 16 times normal. Following splenectomy, the principal mechanisms, the first being the dep- spleen was 'found to weigh more than 700 g. It ression of red cell production, and the second is thus clear that splenomegaly per se is in- the direct destruction of red cells during their sufficient 'to impair erythropoiesis, although passage through the organ. Recent work has this does not-necessarily exclude the possibility tended to focus less attention on the possible of a depressant effect by the spleen in other dyshaemopoietic influence of the spleen and conditions. has emphasized the complexity of the relation- ship between the organ and the circulating red Splenic Destruction in situ cell. The pulp of the spleen consists of venous sinuses between which run the pulp cords of and Billroth. The over the and Splenomegaly Erythropoiesis controversy direction http://pmj.bmj.com/ The possibility of marrow depression arising degree of the blood flow through the cords is from a presumptive humoral influence of the still unresolved, but in man the circulation is spleen (has been frequently considered, for probably of -the mixed variety, both open and instance by Moeshlin (1956), Cohen, Gardner closed channels being present (Weiss, 1959) and Barnett (1961a and b) and Dameshek although the direct sinusoidal pathway is (1960). Motulsky, Casserd, Giblett, Broun and thought to predominate (Prankerd, 1963). Finch (1958), in dismissing such a mechanism, Barnett and Lewis (1961) have pointed out stated that they had never obtained satisfactory that 'the red cells may sometimes pass through on October 6, 2021 by guest. evidence for it, but Wetherley-Mein, Jones and what is functionally a mesenchymal mass, Pullan (1961) have presented radio-iron studies honeycombed with channels lined by reticular of patients with myeloid metaplasia before and cells, which brings the blood cells into close after splenectomy which were consistent with contact with the macrophage system. The an improvement in marrow function following structure is therefore well adapted to be a site removal of 'the spleen. of active erythrophagocytosis. The problem is an especially difficult one to In normal circumstances in man, the spleen evaluate: marrow depression in the presence of plays only a small part in the destruction of splenomegaly, as in lymphomata, acute and red cells, sharing this function with other chronic leukaemias, and the lipidoses, may be components of the macrophage system due to other effects of the disease, especially in (Prankerd, 1963). In many abnormal circum- December, 1965 BOWDLER and PRANKERD: Splenic Mechanisms 749 Postgrad Med J: first published as 10.1136/pgmj.41.482.748 on 1 December 1965. Downloaded from stances, however, the spleen may become the pool, or a balanced interchange between the principal site for the destruction of red cells, pool and the general circulation, in which as shown both by the accumulation of iron in case ;the rate of entry could be much greater. the tissues, and by qthe progressive deposition This arises from the fact that in a steady state, of chromium-51 in the spleen after the intra- any irreversible loss of cells from the general venous injection of labelled red cells (Jandl, circulation must be balanced by an equivalent Greenberg, Yonemoto and Castle, 1956; release of new cells from the bone marrow, Hughes Jones and Szur, 1957; McCurdy and which imposes a constraint on the maximum Rath, 1958). Such a situation may result from rate of loss under such conditions. abnormalities of the endogenous red cells, as Conditions of rapid interchange between the in hereditary spherocytosis or elliptocytosis, or general circulation and the splenic pool can an abnormality mainly in the spleen itself such be demonstrated either by following the second- that normal transfused cells may also be ary rise in splenic radioactivity after the destroyed even in the absence of demonstrable intravenous injection of isotope-labelled cells antibodies, a situation sometimes encountered by means of a scintillation counter (Motulsky, in thalassaemia major. Casserd and Giblett, 1956; Harris, McAlister The concept has arisen of "splenopathic and Prankerd, 1958) or by estimating the anaemia", for instance in leukaemia, in which associated fall in the blood radioactivity the enlarged spleen, by reason of its increased (Motulsky and others, 1958). Simultaneous size, exerts a deleterious and destructive effect measurements of blood and spleen aotivity on the red cell '(Dameshek and Gunz, 1959). It have been found to produce patterns consistent is certainly true that massive splenomegaly is with the concept of two-pool interchange. frequently accompanied by a reduction in the Evidence for irreversible is pooling more diffi- Protected by copyright. red cell lifespan, but this is not necessarily so, cult to obtain, but such a possibility may at least within the limits ,that can be assessed sometimes be inferred (Bowdler, 1962), and in by the chromium-51 method (Bowdler, 1965). some conditions it is olear that both inter- Further, even when shortened survival is pre- changing and irreversible pools are present sent, this is not necessarily corrected by splenec- together. tomy, and a spleen of large size cannot in all Splenic pooling of red cells has been shown instances be held to imply excessive destruction in hereditary spherocytosis, autoimmune hae- within the organ. molytic disease, chronic myeloid leukaemia, thalassaemia major, myeloid metaplasia, perni- Red Cell Pooling cious anaemia, Hodglin's disease and in sickle- In certain haemolytic states the spleen has a cell disease when splenomegaly is present, high red cell content, sometimes representing a although not every case of these diseases will substantial fraction of the total red cell mass. show the phenomenon. Pooling may also occur Such intrasplenic red cells might be considered in the normal spleen when abnormal cells are in the until introduced into the Harris and irreversibly trapped organ destroyed circulation; http://pmj.bmj.com/ in situ. Alternatively, they might be regarded as others (1958) demonstrated this with naturally a population exchanging with the red cells of occurring and artificial spherocytes and with the general circulation. Thirdly, since these antibody-coated cells, while Bowdler (1962) are not mutually exclusive possibilities, some found it to occur with,the cells of a spleneoto- cells might be irreversibly trapped while others mized thalassaemic donor. In many instances could still return to the extrasplenic circulation. in which pooling occurs there are abnormalities For some authors the term "sequestration" in the shape or volume of the red cells, which implies cell trapping by the spleen with sub- may affect the rate of transit of such cells at on October 6, 2021 by guest. sequent destruction of the cells in the organ, the level of the communications between the but in general it is preferable to keep the splenic cords and the sinuses. However, gross difference between pooling and destruction quite changes in the cells are not necessarily present, distinct as the two processes are not necessarily and more subtle alterations of the cell surface, associated. such as the depletion of lipid (Harris, McAlister The spleen may contain a substantial frac- and Prankerd, 1957) or blockade of sulphydryl tion of the total red cells of the body despite groups (Jacobs and Jandl, 1962) are also the absence of progressive anaemia and this effective. must imply either prolonged survival of the It is clear then that in many conditions, the cells before destruction by the organ, with a red cells may spend intermittent periods packed relatively slow rate of entry of cells to the within the pulp of the spleen, a situation which 750 POSTGRADUATE MEDICAL JOURNAL December, 1965 Postgrad Med J: first published as 10.1136/pgmj.41.482.748 on 1 December 1965. Downloaded from in many respects can be regarded as metabo- production of anti-erythrocyte antibodies in lically disadvantageous, as shown by the low autoimmune haemolytic disease. Such an hypo- pH and high lactic acid content of the splenic thesis would account for the reduction in pulp (Murphy, 1962). The possibly deleterious antiglobulin titre of the red cells found in many effects of such an environment have principally cases of this disease after splenectomy. It would been discussed in relation to the hereditary further help to explain the improvement after spherocyte (Young, 1955; Emerson, Shen, Ham, splenectomy in cases in which excessive de- Fleming and Castle, 1956; Prankerd, 1960) and pos;ition of ¢hromium-51 from labelled red the relevance of this to other conditions remains cells in the spleen is not prominent, and in which to be proved. The H.S. cell has widely been it may be supposed Ithat some factor other considered to acquire a residuum of damage than local destruction of cells in Ithe organ during repeated incubations in the splenic pool, must be operating (Bowdler, 1965). which ultimately renders it liable to removal by In this context, it may further be conjectured the reticuloendothellial system. In one subject, that the vascular architecture of the spleen however, who showed marked sphering of cells may, by producing ithe close apposition of the and a large splenic pool of red cells in the target red cell with !the antibody producing course of an au;toimmune haemolytic anaemia, cells, lead effectively Ito the coating of the there was found not only destruction of red former while repeatedly stimulating the latter. cells in the spleen with local storage of the contained isotope, but also evidence of haemo- Dilution Anaemia lysis with release of the isotope to secondary storage in extrasplenic sites, thus suggesting A further mechanism by which anaemia may either 'that there is more 'than one mode of red arise in the presence of an enlarged spleen has cell destruction in such a spleen, or :that the recently been recognised. An investigation of Protected by copyright. haemolytic capacity of the spleen can exceed the anaemia accompanying cryptogenic spleno- the capacity of the organ for storing the pro- megaly in Chinese subjects by MoFadzean, ducts of red cell destruction (Bowdler, 1962). Todd and Tsang (1958a and b) showed a Recently, Rifkind (1964) has studied the spleen haemolytic process which could be corrected by electron microscopy in rabbits in which by splenectomy, Ibut in some cases the haemo- Heinz body anaemia had been induced by globin level was further lowered by expansion phenylhyddrazine. Evidence was obtained in this of the plasma volume, which thus effectively instance also for 'two modes of eryt'hrocyte diluted the red cell mass. The plasma volume destruction, the bulk of 'the cells being destroyed could, however, be reduced by splenectomy, by erythrophagocytosis in the cords, while a though less effectively when there was associated smaller proportion was destroyed by intra- hepatic cirrhosis. vascular lysis in the sinusoids. Similar expansion of the plasma volume with reduction in the level of haemoglobin in the circulating blood was found in a case of Antibody Production Gaucher's disease by Bowdler (1963), and here http://pmj.bmj.com/ The recognition of 'the role of 'the lymphocyte too there was a 'reduction in the plasma volume and the 'plasma cell in the synthesis of immuno- after splenectomy of such a degree that although globulins would imply a significant function for the red cell mass also declined, ithe relative the spleen in antibody production. In the rat, volume of Ithe 'red cells increased. In this it has been shown experimentally that the instance, there was no significant change in the formation of antibody after the intravenous red cell lifespan and correction of the anaemia injection of antigen is initiated by the spleen, could be ascribed entirely to the volume while such 'precedence does not exist when the changes. Similar observations have also been on October 6, 2021 by guest. antigen is introduced by other routes (Rowley, made in cases of myeloid metaplasia and 1950a). Taliaferro and Taliaferro (1952) have chronic myeloid leukaemia (Bowdler, 1965). studied Ithe production of haemolysin to sheep Weinstein (1964) studied five cases of simple red cells in rabbits, and found ithe spleen splenic hyperplasia, two of them associated important in the response Ito the initial and with rheumatoid disease. All patients showed second doses of antigen, but less important a rise in the venous haemaltocrit after splenec- subsequently. In man, Rowley (1950b) has tomy, and in none was 'there a rise in ,the found a marked inadequacy in antibody total mass of Ithe red cells. Contraction of ithe response to injected sheep red cells in splenecto- ,plasma volume was proved in three cases, and mized subjects. There is thus a strong possibility inferred in ithe remainder. that 'the spleen may be a significant site for the The mechanism of the expansion of the Postgrad Med J: first published as 10.1136/pgmj.41.482.748 on 1 December 1965. Downloaded from December, 1965 BOWDLER and PRANKERD: Splenic Mechanisms 751 plasma volume in these cases is not entirely which this is not indicated by the accumulation understood. One possible mechanism is that of isotope to any marked degree by the spleen. the vascular space requiring to be filled with Firstly, 'this may occur when the anaemia is blood may be excessive in the presence of a due ,to the diluting effects of a high plasma large spleen, and thait the marrow in these volume. It is therefore useful ,to measure the conditions 'is insufficiently active to be able red cell mass as part of the chrom'ium-51 to supply sufficient red cells for this to be study, and to confirm the findings by an estimate possible. Consequently, the plasma expands in -of the plasma volume, for instance by the compensation for the relative inadequacy of use of 131I-labelled human serum albumin. The the available red cell mass. The 'tendency of finding of pooling of red cells in the spleen, as the spleen ito concentrate red cells so as to indicated by surface counting over the organ produce a high intrasplen'ic ratio of cells to 'together Iwith interval estimates of the red cell plasma, as shown by Verel (1954), Rothschild, mass, also provides some indication of ineffect- Bauman, Yalow and Berson (1954) and others, ive distribution of athe available red cells. would make splenic enlargement especially Secondly, relief of anaemia may sometimes significant as a drain on 'the available red cell be obtained by splenectomy even when isotope mass. However, ithis cannot be a complete deposition has been prominent in the liver as explanation, since correction of the anaemia well as ;the spleen, and when no dilution effect may 'be delayed for several weeks after splenec- is operating. The reason for 'this is conjectural, tomy, so that some extrasplenic adjustment of but presumably some other function of the the plasma volume must itake place. Whether spleen, such as tits facility for producing anti- this depends on the late changes in the vascu- bodies, may have been critical in the production lature of ithe splenic bed after operation, as of the anaemia. It remains true at the present Protected by copyright. suggested by McFadzean and others (1958b), time, therefore, that the information required or whether {there is a secondary allteration in for a strictly reasoned assessment of the out- the plasma oncotic pressure, as inferred by come of splenectomy on the severity of an Weinstein (1964), remains ito be investigated. associated anaemia is in many cases still in- Discussion accessible. There is now considerable evidence 'that the relationship between the spleen and the red Summary cell is not limited Ito erythrophagocytic destruc- An outline has 'been presented of the tion. In some respects this has complicated the mechanisms by which the spleen may con- problem of deciding on the advisability of ,tribute to ithe production of anaemia. These splenectomv in Ithe individual case. In a few are present to different degrees in individual instances, disease involving the spleen is suffi- cases, and consequently 'the assessment of the ciently constant in its response to removal of importance of Ithe specific factors in any one the spleen 'for 'the decision to be reached with- case may only be possible retrospectively, out difficulty: 'there are, for instance, seldom if at all. The assistance which can be obtained http://pmj.bmj.com/ any doubts as ito the advisability of operation in by available methods of isotope study of red a case of hereditary spherocytosis. Much more cell destruction is considered and the limitations commonly, there is 'the need to assess ithe of the techniques indicated. possible benefit of operation in an individual case, and where Ithis has essentially 'to be REFERENCES assessed in relation Ito the probable effect on BARNETr, C. H., and LEwIS, 0. H. (1961): in "Recent anaemia, mechanisms outlined must Advances in by Goldby, F., and Ithe clearly Anatomy", on October 6, 2021 by guest. be considered. Harrison, R. J. 2nd Series. p. 388. London: J. & A. Churchill. For more than ten years, since 'the method BOWDLER, A. J. (1962): Theoretical Considerations was described by Gray and Sterling (1950), it Concerning Measurement of the Splenic Red Cell has been possible to estimate 'the red cell Pool, Clin. Sci., 23, 182. the chromium-51 tech- BOWDLER, A. J. 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